This invention relates to a method for producing a color filter and more particularly to a color filter advantageously employed as a color liquid crystal display device.
Among the currently employed methods for preparing a color filter, there are a dyeing method consisting in dyeing a transparent substrate with a binder containing dyes and pigments, a printing method and a pigment dispersion method.
Since the dyeing method consists in selectively forming a thin resin film on a substrate with dyes, a resist printing process and a photolithographic process need to be performed each time the color is changed. Although resist printing is unnecessary with the printing method, there is a limit to the refinement of color patterns and, the larger is the number of colors, the printing position becomes the worse. Although the fine color pattern is possible with the pigment dispersion method, a high precision photolithographic process needs to be performed each time the color is changed, resulting in a complicated process.
For overcoming the deficiency, there is proposed in Japanese Laid-open Patent Application No. 59-114572 (1984) a method for producing a color filter by an electrodeposition coating method. With this method, a transparent electrode is prepared by patterning a transparent electrically conductive film deposited on the substrate, and electrical voltage is applied only to a portion of the patterned transparent electrode which is to be dyed in the same color. The substrate is immersed in a colored electrodeposition bath for forming a colored layer by electrodeposition. Electric voltage is then applied only to a portion of the substrate which is to be dyed in a different color, and the substrate is then immersed in a colored electrodeposition bath for forming a different color layer by electrodeposition. However, it is necessary with this method to perform a high precision patterning of the transparent electrode, and to pay meticulous care during the subsequent process not to break the fine pattern, because otherwise the subsequent coloring process is rendered difficult. Besides, the patterned transparent electrode needs to be electrically continuous, even in fine pattern sections, so that limitations are imposed on the degree of freedom of the pattern shape.
In Japanese Laid-open Patent Application No. 63-210901 (1988), there is proposed a method consisting in forming colored layers by light exposure, development and electrodeposition, using a mask having patterns only in areas to be dyed in the same colors and a positive type photosensitive resin composition, and repeating the steps of light exposure, development and electrodeposition a desired number of times. This method is inferior in stability because it makes use of a compound containing unstable quinone diazid groups. Besides, if the quinone diazid compound is brought into contact with an aqueous alkali solution, the quinone diazid compound in the unexposed part is also reacted with an aqueous alkali solution so that photosensitivity is markedly changed to present difficulties in the subsequent light exposure and development steps.
In the aforementioned electrodeposition methods, the transparent electrode for forming colored layers thereon is also employed as an electrode for driving a liquid crystal display device. However, the colored layers formed on the transparent electrode are of dielectric nature so that voltage for driving the liquid crystal device is extremely high. Accordingly, on the practical application another transparent electrode for driving the liquid crystal device is further provided on the colored layers produced in accordance with the aforementioned methods so as to lower the driving voltage. In the meanwhile, as the transparent electrode employed in the aforementioned methods has light transmittance of 80 to 85%, the provision of two transparent electrodes poses another disadvantage in that light transmittance is lowered, leading to inferior performance of a colored display liquid crystal device. To solve such a problem, there is proposed in Japanese Laid-open Patent Application No. 1-22379 a method for forming colored layers on an original plate and transcribing the colored layers on a transparent substrate. In the method, however, the transcription is performed for each color, thus necessitating high precision of alignment at respective transcription steps.
With any of the above methods, high precision processing is required for alignment so that it is difficult to cope with the demand for a larger work size, that is a larger picture size with reduced costs.